Our house has two propane tankless heaters, Rinnai R85's, and we are pleased with them. No issues and quick hot water when needed. Note that our house was built with them as original installations. I believe that the gas flow rate for the tankless geaters is higher than that of a similarly "sized" conventional one so I suggest you confirm your exising gas line is adequate for the required flow. Ours each have key pads that allow temp setting and diagnostics. I have no clue as to how difficult they are to install.
